The present invention relates to light-activated light-emitting devices, and optical amplifiers and regenerators utilizing such devices.
The use of electricity and microwaves for carrying communications is well-known. In recent years, it has been suggested that messages be carried in optical fiber waveguides forming part of communication systems which feature advantageously wide bandwidth, substantial freedom from electromagnetic interference, and attractive cost. In some such systems light-emitting diodes convert electrical information into light signals, and the optical fibers carry the light to its destination. A photodetector receives and converts the light signals to electrical form at the destination.
In more complex systems the electrical signal derived from the photodetector is then amplified by means of electronic apparatus and applied to another light-emitting diode and optical fiber, thus extending the distance over which optical communication can be performed. The photodetector, electronic amplifier and light-emitting diode form an optical repeater.
When the design of the system is such that communications or digital logic information is sent over each optical fiber in the form of short pulses, the pulses are not only reduced in strength on their way, thus requiring amplification, but also are disadvantageously broadened in time by a phenomenon known as optical dispersion which results from the components of the light signal travelling at different velocities. This objectionable pulse broadening has been heretofore eliminated in an optical repeater by providing an electronic pulse regenerator circuit as part of the electronic apparatus between the photodetector and light-emitting diode of the repeater.
Unfortunately, optical communications systems utilizing such prior art repeaters and regenerators can involve substantial expense and consequently in many applications can have difficulty in economically competing with coaxial cable and other electrical transmission systems.